The invention herein relates to solar radiation collectors or conversion devices adapted to gather energy from the sun and transfer collected energy to a heat transfer fluid such as air or water. A great number of such devices have been proposed. Few, if any, however, have achieved wide acceptance since they usually do not sufficiently provide the needed higher efficiencies, economical production costs, and convenience of installation, operation and maintenance to be competitive with other energy souces. Moreover, few, if any, economical and practical devices of this nature are adapted for operation at the high heat transfer fluid temperature levels needed both for greater efficiency or to produce refrigeration based on commonly available cooling systems. Examples of prior art devices may be found in the U.S. Pat. Nos. to C. G. Abbot, 1,801,710; 1,855,815; 1,946,184 and 2,141,330; B. O. Christenson No. 2,469,496 and H. P. Sleeper, Jr. No. 3,125,091.
Among other problems seen in prior art devices are their sometimes weak structural resistance to externally applied pressures, the ability to operate only at no or very low vacuum and a tendency, in those devices employing evacuated chambers to loss of vacuum, all with resultant poor efficiency. Various degrees of vacuum have been employed in solar radiation collectors to decrease heat transfer from a hot area of collection back to the ambient atmosphere. The best efficiencies are achieved with relatively high levels of vacuum, e.g., in the range of about 10.sup.-3 to about 10.sup.-5 torr. Potential vacuum loss is a serious problem since by vacuum depletion efficiency may be impaired to the point that the collector becomes effectively inoperative for its intended use. In certain known collectors the vacuum containing enclosure wall is breached or interrupted by some structure, such as a heat transfer fluid conduit which penetrates or passes through the wall to extract heat. A seal must then be provided at the place of entry of such structure and such seals, particularly over extended time periods are prone to leakage with resultant degradation of vacuum. Moreover, in such prior structures it has frequently not been possible to easily separate the radiation collector portion from the associated heat transfer fluid portions which leads to different or expensive maintenance and repair.